The XLoadFont function loads
the specified font and returns its associated font ID. If the font name
is not in the Host Portable Character Encoding, the result is implementation-dependent.
Use of uppercase or lowercase does not matter. When the characters ``?'' and
``*'' are used in a font name, a pattern match is performed and any matching
font is used. In the pattern, the ``?'' character will match any single character,
and the ``*'' character will match any number of characters. A structured format
for font names is specified in the X Consortium standard X Logical Font
Description Conventions. If XLoadFont was unsuccessful at loading the
specified font, a BadName error results. Fonts are not associated with
a particular screen and can be stored as a component of any GC. When the
font is no longer needed, call XUnloadFont.

XLoadFont can generate
BadAlloc and BadName errors.

The XQueryFont function returns a pointer
to the XFontStruct structure, which contains information associated with
the font. You can query a font or the font stored in a GC. The font ID stored
in the XFontStruct structure will be the GContext ID, and you need
to be careful when using this ID in other functions (see XGContextFromGC).
If the font does not exist, XQueryFont returns NULL. To free this data,
use XFreeFontInfo.

XLoadQueryFont can generate a BadAlloc error.

The
XLoadQueryFont function provides the most common way for accessing a
font. XLoadQueryFont both opens (loads) the specified font and returns
a pointer to the appropriate XFontStruct structure. If the font name is
not in the Host Portable Character Encoding, the result is implementation-dependent.
If the font does not exist, XLoadQueryFont returns NULL.

The XFreeFont
function deletes the association between the font resource ID and the
specified font and frees the XFontStruct structure. The font itself will
be freed when no other resource references it. The data and the font should
not be referenced again.

XFreeFont can generate a BadFont error.

Given
the atom for that property, the XGetFontProperty function returns the
value of the specified font property. XGetFontProperty also returns
False if the property was not defined or True if it was defined. A
set of predefined atoms exists for font properties, which can be found
in <X11/Xatom.h>. This set contains the standard properties associated with
a font. Although it is not guaranteed, it is likely that the predefined
font properties will be present.

The XUnloadFont function deletes the
association between the font resource ID and the specified font. The font
itself will be freed when no other resource references it. The font should
not be referenced again.

The
XFontStruct structure contains all of the information for the font and
consists of the font-specific information as well as a pointer to an array
of XCharStruct structures for the characters contained in the font. The
XFontStruct, XFontProp, and XCharStruct structures contain:

X supports single byte/character, two bytes/character matrix, and 16-bit
character text operations. Note that any of these forms can be used with
a font, but a single byte/character text request can only specify a single
byte (that is, the first row of a 2-byte font). You should view 2-byte fonts
as a two-dimensional matrix of defined characters: byte1 specifies the range
of defined rows and byte2 defines the range of defined columns of the font.
Single byte/character fonts have one row defined, and the byte2 range specified
in the structure defines a range of characters.

The bounding box of a character
is defined by the XCharStruct of that character. When characters are
absent from a font, the default_char is used. When fonts have all characters
of the same size, only the information in the XFontStruct min and max
bounds are used.

The members of the XFontStruct have the following semantics:

·

The direction member can be either FontLeftToRight or FontRightToLeft.
It is just a hint as to whether most XCharStruct elements have a
positive (FontLeftToRight) or a negative (FontRightToLeft) character
width metric. The core protocol defines no support for vertical text.

·

If
the min_byte1 and max_byte1 members are both zero, min_char_or_byte2 specifies
the linear character index corresponding to the first element of the per_char
array, and max_char_or_byte2 specifies the linear character index of the
last element.

If either min_byte1 or max_byte1 are nonzero, both

min_char_or_byte2
and max_char_or_byte2 are less than 256, and the 2-byte character index
values corresponding to the per_char array element N (counting from 0)
are:

If the per_char pointer is NULL, all
glyphs between the first and last character indexes inclusive have the
same information, as given by both min_bounds and max_bounds.

·

If all_chars_exist
is True, all characters in the per_char array have nonzero bounding
boxes.

·

The default_char member specifies the character that will be used
when an undefined or nonexistent character is printed. The default_char
is a 16-bit character (not a 2-byte character). For a font using 2-byte matrix
format, the default_char has byte1 in the most-significant byte and byte2
in the least significant byte. If the default_char itself specifies an undefined
or nonexistent character, no printing is performed for an undefined or
nonexistent character.

·

The min_bounds and max_bounds members contain the
most extreme values of each individual XCharStruct component over all
elements of this array (and ignore nonexistent characters). The bounding
box of the font (the smallest rectangle enclosing the shape obtained by
superimposing all of the characters at the same origin [x,y]) has its upper-left
coordinate at:

The ascent member is the logical extent of the font above the baseline
that is used for determining line spacing. Specific characters may extend
beyond this.

·

The descent member is the logical extent of the font at or
below the baseline that is used for determining line spacing. Specific characters
may extend beyond this.

·

If the baseline is at Y-coordinate y, the logical
extent of the font is inclusive between the Y-coordinate values (y - font.ascent)
and (y + font.descent - 1). Typically, the minimum interline spacing between
rows of text is given by ascent + descent.

For a character origin at [x,y],
the bounding box of a character (that is, the smallest rectangle that
encloses the character's shape) described in terms of XCharStruct components
is a rectangle with its upper-left corner at:

0
0>=40 .vs 0u
0<=39 .vs 0p
[x + lbearing, y - ascent]

Its width is:

0
0>=40 .vs 0u
0<=39 .vs 0p
rbearing - lbearing

Its height is:

0
0>=40 .vs 0u
0<=39 .vs 0p
ascent + descent

The origin for the next character is defined to be:

0
0>=40 .vs 0u
0<=39 .vs 0p
[x + width, y]

The lbearing member defines the extent of the left edge of the character
ink from the origin. The rbearing member defines the extent of the right
edge of the character ink from the origin. The ascent member defines the
extent of the top edge of the character ink from the origin. The descent
member defines the extent of the bottom edge of the character ink from
the origin. The width member defines the logical width of the character.